PHOTOEMISSION-STUDIES OF TIME-RESOLVED SURFACE-REACTIONS - ISOTHERMAL DESORPTION OF CO FROM NI(111)

A new dynamic approach to spectroscopic studies of surface reactions is described. A fast-acting UHV gas dosing system is employed to prepare the adsorbed species in an initial chemisorption state under reaction conditions of elevated temperature and/or pressure (to ∼ 1 Torr). Individual reaction steps are then resolved in time using photoemission spectroscopy to probe the surface electronic structure, yielding information about the kinetics of individual reaction steps, the nature of chemisorbed species, and the surface reaction path. As a first application of this approach, the kinetics of isothermal desorption of CO from Ni(111) is studied for temperatures up to ∼230°C. The coverage-dependence of the rate constants is revealed directly in the shape of each desorption curve. Preexponential (frequency) factors as well as desorption activation energies show significant variation with coverage. © 1979.